Method of machining bevel gears



Aug 1935 J. c. DRADER ET AL. ZMQAQZ METHOD OF MACHINING BEVEL GEARS Filed Dec. 4, 1955 2 Shams-Sheet l ATTOR N EYS.

1936. J. c. DRADER ET AL 2,049,492

METHOD OF MACHINING BEVEL GEARS Filed Dec. 4, 1933 2 Sheets-Sheet 2 INVE R6. Josey/r Zradsn /Yevr y. Q. M02727.

MQZM M ATTORN EYS.

Patented Aug. 4, 1936 2,049,492

UNITED STATES PATENT OFFICE METHOD OF MACHINING BEVEL GEARS Joseph C. Drader and Henry Q. Munn, Detroit, Mich., assignors, by mesne assignments, to Michigan Tool Company, a corporation of Delaware Application December 4, 1933, Serial No. '700,850

1 Claim. (Cl. 905) Our invention relates to bevel gears and parthey are relatively moved along a plane parallel ticularly to the method of machining bevel gears to the plane of the root of the teeth; to machine bya multi-toothed cutting tool. a true bevel tooth from the front to the rear Difficulty has always been experienced heretoof the blank by taking advantage of the pro- 5 fore in machining bevel gears due to the fact gressive change in peripheral speed of the blank 5 that the pitch diameter of the teeth is conduring such movement to have the portions of stantly changing from the front to the rear end the composite cutting edges shape the tooth at of the bevel gear. It has been the practice to the point corresponding tothe varying pitch dimachine straight bevel gears by indexing each ameters; and, in general, to provide a method l0 tooth and passing a cutter thereacross and emfor cutting bevel gears which is simple in operaploy a plate-like cutter for the spiral type of tion, which employs a single position tool and bevel gears. which produces accurate bevel gears. v

.In practicing the present invention av tool of Other objects and features of novelty of our the hob type is employed having teeth thereon invention will be. either specifically pointed out 5 the sides of some of which have a cutting edge or will become apparent when referring, for a which is a composite of some or all of the varybetter understanding of our invention, to the ing pitch diameter of the bevel gear tooth at following description taken in conjunction with various points in its length. The hob is mountthe accompanying drawings, wherein:

ed on a rotatable spindle, it being a single posi- Figure 1 is a view in elevation of a cutting tion cutting tool, and the gear is mounted to tool operating on a bevel gear in accordance have the root of the teeth disposed normal to with our invention,

the axis ofthecutting toolwith the axis of the Fig. 2 is asectional view of a bevel gear to bevel gear at an angle tosuch normal. The be cut by our method, bevel gear and hob are moved relative to each Fig. 3 is a plan view of a cutting tool employed 251. other, parallel to the root of the teeth, during to form a portion of the teeth of, the tool illusthe time they are rotated in synchronism with trated in Fig. 1,

each other. The cutting of the various pitch Fig. 4 is a sectional view of a bevel gear being diameters on the gear blank is effected because Operated on by our cutting tool, of the change of pitch diameters of the gear Fig. 5 is a diagrammatic view of a machine disblank relative to the cutting teeth of the hob closing the method of operation of the tool on 30 during their relative movement. It will be seen the blank,

that, although the rotation of the hob and the Fig. '6 is a further method of machining a gear blank is constant relative to each other, bevel gear blank which embodies the method of the peripheral speed of the gear blank is changour invention,

1 ing throughout all points of the length of the Fig. 7 is an end view of the structure illustrated teeth. This is due to the varying pitch diamin Fig. 6, and

eter. In the presence of such'variation in the Fig. 8 is a diagrammatic View of a machine emperipheral speed of the bevel gear the cutting ployed to operate the tool and work blank illusedges having a composite form will be available trated in Figs. 6 and '7.

40 to cut the particular form on' the teeth corre- In our copending application, Serial No. sponding to the pitch diameter of the point. 693,228, filed October 6, 1933, and assigned to In this manner a. true toothed form of varying the assignee of the present invention, we have Ditch diameter Will be cut 011 e bevel gear described and claimed the hob as a cutting tool, during the single passage of the single position employed to produce bevel gears in accordance hob thereacross. with the present method. The hob I0 is ma- A n y, a n bje ts of our invenchined by a plurality of cutting tools I I and I2, tion are to employ a Single position Cutting tool the profile of. the cutting edges of which correfor machining the teeth on a bevel gear through spondto that at various points along a tooth IS the single passage of. the tool thereacro'ss; to of a bevel gear l4, illustrated in Fig. 2. The root provide a hob having a plurality of teeth therediameter at the point l5 on the bevel gear I4 is 50 on, some of which have cutting edges of a comselected for the cutter l l, the radius of which is posite form of different tooth forms taken at indicated by the line It normal to the root ll of various points along the tooth to be produced the teeth of the bevel gear. The cutter II has a thereby; to operate the hob and bevel gear in root diameter, the radius of which is indicated synchronism' with each other during the time by the line l8, being a line perpendicular to the 55 crown IQ of the tooth l3 of the bevel gear. The hob I0 is cut in the ordinary manner by the cutter I l, both being operated in synchronism with each other during the passage of the cutter across the hob.

In Fig. 3, we have illustrated a cutter I2 which represents the cutter corresponding to the root diameter at the section 2! of the hob l4 illustrated in Fig. 2 which may alone be employed with the hob l I when only a rough form of bevel gear is desired. When accurate bevel gears are to be machined, more cutters are employed selected at points indicated by the lines 22, 23, and

24 on the gear of Fig. 2. The various cutters are employed subsequently to each other, preferably relative to the sizes, resulting in some of the teeth being further out in the shape of the form of the cutters at the various sections 2|, 22, 23, and 24. This is effected due to the change in peripheral speeds of the cutters when the cutters are mounted on the shaft on which the cutter l l is mounted and moved toward the hob- I!) in accordance with the change of pitch diameter of the tooth. The tooth is mounted on. the centerline of the hob adjacent to the female tooth cut in the hob blank by the cutter l and spaced from both sides thereof so that it will not deform such teeth out by the cutter ll. However, due to the change in the peripheral speed of the cutter, the teeth will lag relative to the advance of the hob teeth until they out certain amounts from some of the teeth of the hob. After all of the cutters'have been employed, some of the teeth of the hob will have a composite form of all of the teeth of v the cutters. 7

After such hob is formed it is only necessary to pass the hob across the surface of the blank of the bevel gear to produce teeth thereon. In Figs. 4 and 5, we have illustrated'the employment of a single hob ID, the teeth 26 thereof being radially relieved, that is to say, the shape of the teeth are retained throughout but are shortened radially so that relief is provided to the cutting edge, and thetooth form isrmaintained as the front cutting edge is machined away during a sharpening operation. The hob l0 and the blank 21' to be machined are mounted on arbors inthe same manner as the cutter I] was mounted relativeto the hob Hi out thereby. A relative movement is provided between the bevel'gear 21 and the cutter IE3 in a plane parallel to the'root l1 of the gear sothat the various peripheral speeds will be present during the passageof the gear and cutter blank relative to each other so that at such points the portion of the composite tooth of the cutter representing the profile at that point will be available to machine that form on the tooth of the bevel gear. In this manner a true bevel gear tooth is machined throughout the blank during a single passage of the cutter l9 relative to the blank 21 in a path parallel to the root of the tooth.

In Fig. '5, we have illustrated diagrammatically a machine with the cutter I0 and the blank 21 rotated in synchronism with each other during the time a relative movement is provided between the cutter and blank 21. A shaft'28 is driven through a pulley 29 to operate a bevel gear 3| which is mounted in mesh with a bevel gear 32 both of which are carried along by supporting brackets 29. The gears are driven by means of a key (not shown) which meshes with a splineway 33 provided in the shaft 28; The gear 32 drives a spindle 34 upon which the bevel gear blank 21 is retained by a nut 35.- The'bevel gear usually is provided with a splineway which mates with a key on the spindle 34 and is retained in fixed relation relative thereto. A gear 36 is likewise driven by the shaft 28 which operates through gears 31 and 38 to drive a gear 33 which is secured to a shaft 4| which drives a bevel gear 42 mated with a bevel gear 43 which drives the arbor 44 upon which the cutter II] is mounted. The gears 32 and brackets 29 are mounted ona table 45 which is driven by a lead-screw 46 by means of a hand wheel 41, although we preferably drive the table automatically by means well known in the art. In this manner it is only necessary to secure a blank on the spindle 34 and operate the machine to have the-hob l0 rotate in synchronism with the rotation of the gear blank 21 during the time the table 45 is moved relative to the cutter If! to completely cut a bevel gear from the blank. This operation is exceedingly fast and surprisingly accurate, and is a considerable advance in the art in the method of machining bevel gears.

Asa further extension of our invention we have illustrated in Figs. 6, '7, and 8, a method wherein two cutters 50 are employed which are similar to each other but whichhave'the teeth 5i thereof sidewardly relieved rather than relieved radially as illustrated on the cutter IQ of Fig. 4. In this manner thewidth of the tooth is reduced relative to the front cutting edgebut the side form retained throughout the length of the tooth. However,'the disadvantage of this construction resides in the factthat the machiningof the front cutting edges of the teeth 5| to sharpen the edges results in the tooth 5|. being of less width than the actual slotto becut between the teeth of the blank as a result of Which the bevel gear teeth [3 will be of greater width than desired; To overcome this objectional' feature we have employed twoof the cutters 50 mounted in such manner that'one cutter cuts on one side of a tooth during the timetheother cutter cuts on the opposite side of a tooth which provides a further advantage of balancing the torque on the arbor supporting the bevelgear blank 21. The cutters are driven in synchronismwith each other and with the rotation of the bevel gear 21, and are moved on diverging. axes which form an angle equal to the angle between theroots ll of the bevel gear. In this manner the cutters are moved parallel tothe root ofthe teeth and the changing pitch diameters of the blank are present in the same manner as in the construction illustrated in Figs. 4 and5 heretofore explained.

In Fig. 8, we have illustrated diagrammatically a machine fordriving the gear and cutters in synchronismi with'each other. during the time they are relatively moved across'the face of the blank. Apulley 53 drives a shaft 54 upon which a gear 55 is mounted for driving a gear 52 secured to the spindle 5B which supports the gear blank 21. The gear blank is retained on the spindle 56 by the nut 35 as above explained. The shaft 54 also drives a gear 51 which in turn drives a gear 58 and a shaft 59 upon which a bevel gear BI is mounted. The bevel gear 6| is mated with gears 62 and 63 which drive shafts 64 and 65 to operate through a set of bevel gears 66 to drive the cutters 55 in timed relation to each other and to the rotation of the gear blank 21. Lead screws 61 engage the carriages 68 upon which the cutters 50 are'rnounted and are driven through gears 69 by a gear 10 which may be operated through the driving means of the machine to advance the cuttersa predetermined rate across the blank.

We have illustrated a hand wheel H for effecting the operation in the diagrammatic showing.

To relatively move the gear blank and the cutters after a sharpening operation, we have 11- lustrated nuts 12 on shafts 13 which support the gears through the adjustment of which the cutters are shifted toward the gear blank 21 after the cutters have been sharpened. This shift is made an amount equal to half the reduction of the width of the teeth due to the sharpening operation and in this manner a true tooth form is cut on the bevel gear irrespective of the reduction in width of the teeth on the cutting tools 50 due to the sharpening operation. The gear blank can be moved relative to the cutters, but we prefer to adjust the cutters since the sharpening operation may have changed the tooth width disproportionate amounts.

In this manner, the teeth on the bevel gear 21 are accurately and rapidly machined during one passage of the cutters thereacross after which the bevel gear is removed, the cutters returned to their original position and a new gear blank secured to the shaft and the operation repeated.

While we have described and illustrated but two embodiments of our invention, it will be apparent to those skilled in the art that various changes, omissions, additions and substitutions may be made therein without departing from the spirit and scope of our invention, as set forth in the accompanying claim.

-We claim as our invention;

The method of machining bevel gears utilizing a cutting tool having a plurality of teeth congruent in form to the teeth to be cut and disposed in an overlapping spiral row, said respective teeth having cutting edges which vary progressively in form in accordance with the variation in pitch diameter of the blank from one end thereof to the other which comprises: mounting said cutting tool and a blank in positions fixed against relative bodily movement except in a direction axially of the blank, rotating the tool and blank in synchronism with each other, one face of a tooth of said blank being planed by a cutting edge in one overlapped part of said spiral of the blank, to thereby cause the tool to out said blank teeth to correct form and pitch.

JOSEPH C. DRADER. HENRY Q. MUNN. 

